Why my caesar cipher encryption in java returning symbols

Question

I have been trying to encrypt this from past three days, and the result is all symbols. I dont know where my program is wrong, and i have to submit this as my assignment in one day. desperately need help in this regard. My program takes in input as a text file ,encrypts it with a key and returns the output in another text file.

import java.util.Scanner;
import java.io.FileReader;
import java.io.BufferedWriter;
import java.io.FileWriter;*/
import java.io.*;
import java.lang.*;

public class trial
{
    public static void main(String arg[])
    {
        String textFile="plaintext.txt";
        String cipheredFile=" ciphertext.txt";
        String line= null;
        String letters="";
        String output="";


        int swvalue;
        Scanner input= new Scanner(System.in);
        System.out.println("Select 1: Encrypt, 2: Decrypt, 3: Get Frequency");
        int msg= input.nextInt();
        swvalue= Integer.valueOf(msg);

        switch(swvalue)


        {
        case 1:
            System.out.println("Encrypting the file");
            System.out.println(" Please enter a value for key");
            int keyvalue= input.nextInt();

            try{
            FileReader fileReader=new FileReader(textFile);
            BufferedReader bufferedReader=new BufferedReader(fileReader);

            FileWriter fileWriter= new FileWriter(cipheredFile);
            BufferedWriter bufferedWriter= new BufferedWriter(fileWriter);

            while(( line=bufferedReader.readLine())!=null)
            { 

            char[] toEncrypt=line.toCharArray();

                for(int i=0;i<toEncrypt.length;i++)
                {
                    char alphabet=toEncrypt[i];
                    alphabet=(char) ((alphabet+keyvalue)%26);   
                    letters= String.valueOf(alphabet);  
                    output+=letters;

                }                                                   

        bufferedWriter.write(output);   
             bufferedWriter.newLine();
            }

            bufferedReader.close();                                                         


            //bufferedWriter.close();
            break;
            } catch (IOException e)
            { e.printStackTrace();} 


        case 2:


            System.out.println("Decrypt the file");
            break;



        default:

            System.out.println(" Get frequency");
            break;

        }
    }
}

Its probably character codes. Have a look at an ascii table – D. Ben Knoble Oct 10 '15 at 23:05 — D. Ben Knoble, Oct 10 '15 at 23:05
Did my answer help you in any way? – Yassin Hajaj Oct 11 '15 at 10:29 — Yassin Hajaj, Oct 11 '15 at 10:29

score 1 · Answer 1 · answered Oct 10 '15 at 23:13

Replace this line :

alphabet=(char) ((alphabet+keyvalue)%26);

With this one :

alphabet=(char) ((alphabet+keyvalue)%26 + 'a');

You were actually using the characters from the very bottom of the ASCII characters table. When adding the value of the a character, you're starting again from the begin of the alphabet.

Why my caesar cipher encryption in java returning symbols

1 Answers1